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Ch 29: Plants and the colonization of Land
Ch 30 quiz
Lecture notes
Plants appeared on land about 425 million years ago, and the evolutionary history of the plant kingdom reflects increasing
adaptation to the terrestrial environment.
1. Structural and reproductive adaptations that made the colonization of land possible:
An overview of plant evolution
A. General characteristics of Plants
1. Plants are multicellular eukaryotes that are photosynthetic autotrophs. They share the following characteristics
with their green algal ancestors:
a. chloroplasts with the photosynthetic pigments: chlorophyll a, chlorophyll b, and carotenoids
b. all walls contain cellulose (a glucose polymer)
c. food and energy reserves stored as starch plastids (internal membrane bound organelles)
2. As plants adapted to terrestrial life, they evolved complex bodies with cell specialization for different functions that
distinguishes them from the algae.
a. Aerial plant parts are coated with a waxy cuticle that helps prevent desiccation
b. Though gas exchange cannot occur across a waxy cuticle, O2 and O2 can diffuse between the leaf's interior
and surrounding air through stomata, microscopic pores on the leaf's surface
c. Secondary products: from metabolic pathways not common in all plants that these land plants use are
cuticle waxes, lignin and sporopollenin (on cuticle, a hart part of the shoot and the hard covering on spores and
pollen)
B. The embryophyte condition
1. With the move from an aquatic to terrestrial environment, a new mode of reproduction was necessary to solve
two problems
a. Gametes must be dispersed in a nonaquatic environment. plants produce gametes within gametangia,
organs with protective jackets of sterile (nonreproductive ) cells that prevent gametes form drying out. The
egg is fertilized within the female organ
b. Embryos must be protected against desiccation. The zygote develops into an embryo that is retained
for awhile within the female gametangia's jacket of protective cells. Emphasizing the terrestrial
adaptation, plants are often referred to as embryophytes
C. Alternation of Generations: review
Most plants reproduce sexually and most are also capable of asexual propagation. All plants have life cycles with an
alternation of generations (remember protozoan sex?)
1. A haploid gametophyte generation produces and alternates with a diploid sporophyte generation. The
sporophyte, in turn produces gametophytes
2. The life cycles are Heteromorphic: that is sporophytes and gametophytes differ in morphology (look different)
3. the sporophyte is larger and more noticeable than the gametophyte in all plants but mosses and their relatives
D. Analysis of life cycles within plant divisions tells us the following:
1. Evolutionary trend: reduction of the haploid gametophyte generation and dominance of the diploid sporophyte
2. certain life cycle features are adaptations to a terrestrial environment: (example) replacement of flagellated
sperm by pollen.
E. Highlights of plant phylogeny
1. Their are four major periods of plant evolution that opened new adaptive zones on land:
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a. origin of plants from aquatic ancestors (probably green algae) in the Silurian (475 mil years ago).
(1) cuticle and jacketed gametangia evolved that protected gametes and embryos
(2) Vascular tissue evolved with conducting cells that transport water and nutrients throughout the plant
2. diversification of seedless vascular plants, such as ferns, during the early Devonian about 400 mya.
3. origin of the seed near the end of the Devonian about 350mya
a) seed = plant embryo packaged with a store of food within a protective coat
b) early seed plants bore seeds as naked structures and evolved into gymnosperms including conifers
c) conifers and ferns coexisted and dominated the landscape for more than 200 million years
4) Emergence of flowering plants during he early Cretaceous, abut 130 mya
a) Unlike gymnosperms, flowering plants bear seeds within the flower's protective ovaries
b) Currently the most successful /adapted plants are flowering plants or Angiosperms.
F. Classification in plants: the Major taxonomic category of plants is the Division: it is comparable to phylum, the highest
category in the animal kingdom
A classification of plants
common name Number of existing species
Nonvascular Plants
Division Bryophyta Mosses 12,000
Division Hepatophyta Liverworts 6,500
Division Anthocerophyta Hornworts 100
Vascular Seedless Plants
Division Lycophyta Club mosses, Lycophytes 1000
Division Sphenophyta Horsetails 15
Division Pterophyta Ferns 12,000
Vascular Seed Plants
Division Coniferophyta Conifers 550
Division Cycadophyta Cycads 100
Division Ginkgophyta Ginkgo 1
Division Gnetophyta Gnetae 70
Division Anthophyta Flowering plants 250,000
2. Plants probably evolved form green algae called charophytes
A. Green algae are likely the photosynthetic protists most closely related to plants. This conclusion is based on
homologies in
1) Cell wall composition
2) Structure and pigmentation of chloroplasts
B. Available evidence supports the hypothesis that plants and green algae called charophytes both evolved from a common
ancestor. Researchers have found the following homologies between charophytes and plants:
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1) Both have homologous chloroplasts
a) green algae and plants both have the accessory pigments, chlorophyll b and beta carotene
b) green algae and plants both have chloroplasts with thylakoid membranes stacked as grana
c) compared to chloroplast DNA of various green algae, plant chloroplast DNA most closely matches that of
charophytes
2) Biochemical similarity
a) Most green algae and plants contain cellulose in their cell walls. charophytes are the most plantlike in wall
composition with cellulose making up 20% to 26% of the wall material
b) charophytes peroxisomes are the only algal peroxisomes with the same enzyme composition as plant
peroxisomes
3) Similarity in mitosis and cytokinesis During cell division in charophytes and pants:
a) the nuclear envelope completely disperses during late prophase
b) the mitotic spindle persists until cytokinesis begins
c) cell plate formation during cytokinesis involves cooperation of microtubules, actin microfilaments and
vesicles
4) Similarity in sperm ultrastructure charophyte sperm ultrastructure is more similar to certain plants than to other
green algae
5) Genetic relationship DNA and rRNA similarities in charophytes and plants provides additional evidence for the
hypothesis that charophytes are the closest relatives of plants
A. The origin of alternation of generations in plants
1) The alternation of haploid and diploid generations apparently evolved independently among various groups of
algae
a) since alternation of multicellular haploid and diploid generations does not occur among modern charophytes,
it is presumed that alternation of generation in plants has had a separate origin form alternation of generations
in other algal groups. The zygote is the only diploid structure.
b) the appearance of alternation of generations in plants in thus analogous, not homologous to the alternation of
generations observed in various groups of algae
2) How did alternation of generations evolve in plant ancestors? Coleochaete, a modern charophyte, holds some
clues:
a) The Coleochaete thallus is haploid
(1) in contrast to most algae, the parental thallus of Coleochaete retains the eggs, and after fertilization,
the zygotes remain attached to the parent.
(2) Nonreproductive cells of the thallus grow around each zygote, which enlarges, undergoes meiosis,
and releases haploid swimming spores
(3) haploid spores develop into new individuals
(4) the only diploid stage is the zygote: there is no alternation of multicellular diploid and haploid
generations
b) If an ancestral charophyte delayed meiosis until after the zygote divided mitotically there would be a
multicellular diploid generation (sporophyte) still attached to the haploid parent (gametophyte) such a life
cycle would be an alternation of generations
c) if specialized gametophyte cells formed protective layers around a tiny sporophyte this hypothetical
ancestor would also be a primitive embryophyte
3) What would the adaptive advantage of delaying meiosis and forming a mass of diploid cells? It may maximize
the production of haploid spores
a) If the zygote undergoes meiosis directly, each fertilization event results in only a few haploid spores
b) mitotic division of the zygote form of a multicellular sporophyte amplifies the sexual product. Many
diploid cells can undergo meiosis producing a large number of haploid spores, enhancing the chances of
survival in unfavorable environments
D. Adaptations to shallow water were preadaptations for living on land.
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1) many modern charophytes live in shallow water and some ancient charophytes man have also lived in
shallow water habitats subject to occasional drying
2) about 440 mil years ago, during the transition from Ordovician to Silurian repeated glaciation and climatic
changes caused fluctuations in the water levels of lakes and ponds
3) natural selection may have favored shallow water plants tolerant to periodic drying. Adaptations to
shallow water may have also have been preadaptive for terrestrial life. For example
a) Waxy cuticles
b) protection of gametes
c) protection of developing embryos
4) Eventually, accumulated adaptations made it possible for ancestral plants to live permanently above the water
line, opening a new adaptive zone with
a) sunlight unfiltered by water and algae
b) soil rich in minerals
c) absence of terrestrial herbivores
3. Bryophytes are embryophytes that generally lack vascular tissue and require environmental water to reproduce
A. The Bryophytes include plants found in three divisions:
1) Bryophyta ( mosses)
2) Hepatophyta (liverworts)
3) Anthocerophyta (hornworts)
B. Bryophytes have two adaptations that made the move onto land possible:
1) A waxy cuticle that prevents desiccation
2) Gametangia that protect developing gametes
a) Antheridium, or male gametangium, produces flagellated sperm cells
b) Archegonium, or female gametangium, produces a single egg: fertilization occurs within the archegonium, and
the zygote develops into an embryo within the protective jacket of the female organ (embryophyte condition).
C. Bryophytes are not totally free from their ancestral aquatic habitat
1) they need water to reproduce. Their flagellated sperm cells must swim form the antheridium to the archegonium to
fertilize the egg
2) Most have not vascular tissue to carry water form the soil to aerial plant parts: they imbibe water and distribute
throughout the plant by the relatively slow processes of diffusion, capillary action, and Cytoplasmic streaming
D. Bryophytes lack woody tissue and cannot support tall plants on land: they may sprawl horizontally as mats, but always
have a low profile. Water is moved by diffusion, capillary action and cytoplasmic streaming.
E. Mosses (Division Bryophyta)
1) A tight pack of many moss plants form a spongy mat that can absorb and retain water
a) each plant grips the substratum with rhizoid, long cells or cellular filaments
b) photosynthesis occurs mostly in the small stem like and leaf like structures found in upper parts of the plant:
these structures only share a name with stems and leaves in vascular plants
c) cover about 3% of the land surfaces, and contain vast amounts of organic carbon.
2) There is an alternation of haploid and diploid generations in the moss life cycle (gametophyte is dominant)
a) The sporophyte (2n) produces haploid spores by meiosis in a sporangium, the spores divide by mitosis to form
new gametophytes
b) contrary to the life cycles of vascular plants, the haploid gametophyte is the dominant generation in mosses
and other bryophytes. Sporophytes are generally smaller and depend on the gametophyte for water and
nutrients.
F. Liverworts (division Hepatophyta)
1) Usually less conspicuous than mosses, liverworts:
a) Sometimes have bodies divided into lobes.
b) Have a life cycle similar to mosses. Their sporangia have elaters, coil shaped cells that spring out of the
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capsule and disperse spores.
c)Can also reproduce asexually from gemmae (small bundles of cells that can bounce out of cups on the surface
of the gametophyte when hit by rainwater).
G. Hornworts (division Anthocerophyta)
1) resemble liverworts, but sporophytes are horn-shaped, elongated capsules that grow form the mat like gametophyte.
2) Their photosynthetic cells have only one large chloroplast, unlike the many smaller ones of the other plants.
3) recently shown to be closer to vascular plants by molecular evidence
4. The origin of vascular tissue was an evolutionary breakthrough in the colonization of land
A. Adaptations for terrestrial life in vascular plants
1) Regional specialization of the plant body> Unlike aquatic environments, terrestrial environments spatially
segregate the resources of water and light. This problem was solved as plants evolved subterranean roots that
absorb water and minerals form the soil and an aerial shoot system of stems and leaves to make food
2) Structural support> In aquatic environments, the denser medium of water buoys plants up toward the light, but in
terrestrial environments plants must have structural support to stand upright in air. Such support was provided as
the hard material lignin was embedded in to the cellulose matrix of cell walls
3) Vascular system> Regional specialization of the plant body presented the problem of transporting substances
between the root and shoot systems. This problem was solved as a vascular system evolved with two types of
conducting tissues:
a) Xylem+ Complex plant vascular tissue that conducts water and minerals form the roots to the rest of
the plant
(1) Is constructed of dead, tube shaped cells that form a microscopic water pipe system.
(2) The cell walls are usually lignified(support molecule of plant), giving the plant structural support.
b) Phloem = plant vascular tissue that conducts food throughout the plant.
(1) composed of living cells arranged into tubules
(2) distributes sugars, amino acids and other organic nutrients
4) Pollen, Pollination eliminated the need for water to transport gametes.
5) Seeds, a living embryo with a storage of food, so the plant has time to develop specialized structures.
6) Increased dominance of the diploid sporophyte
B. The earliest vascular plants: large sporophytes amplified the production of spores
1) Oldest fossilized vascular plant is Cooksonia which is dated to the late Silurian.
a) discovered in both European and north American Silurian rocks: North America and Europe were probably
connected during the late Silurian about 4-8 million years ago.
b) It was a simple plant with dichotomous branching and bulbous terminal sporangia on some stems.
c) True roots and leaves were absent: the largest species was about 50cm tall.
d) It grew in dense strands around marshes, a lot like modern moss
e) As the vascular plants become more widespread new species appeared.
5. Ferns and other seedless vascular plants inhabited Carboniferous "coal forests" The earliest vascular plants were
seedless and they dominated the Carboniferous forests. Modern flora include the four divisions of seedless vascular
plants
At about the time of Cooksonia the sporophyte (diploid) generation emerged as the larger and more complex plant
form.
Vascular plants display two distinct reproductive strategies
Homosporus plants produce a single type of spore (have bisexual gametophytes)
heterosporus plants produce two kinds of spores.
A. Division Lycophyta (lycopods)
1) The division Lycophyta included the club mosses and ground pines
a) They initiated in the Devonian period and dominated land during the Carboniferous period (340-280)mya
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b) Some species are temperate (can survive winter), low growing plants with rhizomes and true leaves.
c) Some species are epiphytes, that grow on another organism but are not parasites. (airplants do no harm
d) some species of Lycopodium are born on sporophylls, leaves specialized for reproduction. In some,
sporophylls are clustered at the branch tips into club shaped strobili hence the name club moss
e) spores develop into inconspicuous gametophytes. The non photosynthetic gametophytes are nurtured by
symbiotic fungi
2) Most are homosporus (making only one type of spore which develops into a bisexual gametophyte).
3) Genus Selaginella is heterosporous, having megaspores which develop into gametophytes bearing archegonia, and
microspores which develop into gametophytes with antheridia. The gametophytes are unisexual either male or
female
Homosporous sporophyte single type of spore--- bisexual gametophyte develops into both eggs and sperm
Heterosporus sporophyte develops into two separate gametophytes that produce eggs and sperm separately
B. Division Sphenophyta (Horsetails)
1) The division Sphenophyta includes the horsetails: survived through the Devonian, was dominant during the
Carboniferous period
2) The only existing genus is Equisetum, which:
a) lives in damp locations and has flagellated sperm
b) is Homosporous
c) has a conspicuous sporophyte generation
d) has photosynthetic, free living gametophytes (not dependent on sporophyte for food)
C. Division Pterophyta (Ferns): appearing in the Devonian, ferns radiated into diverse species that coexisted with tree
lycopods and horsetails in the great Carboniferous forests.
1) Most diverse in the tropics, ferns are the most well represented seedless plants in modern floras: there are more
than 12,000 existing species of ferns.
2) Fern leaves are generally much larger than those of lycopods and probably evolved in a different way.
a) lycopods have microphylls, small leaves that probably evolved as an emergence from the stem that contained
a single strand of vascular tissue.
b) Ferns have megaphylls, leaves with a branched system of veins. Megaphylls probably evolved from webbing
formed between separate branches growing close together.
3) Most ferns have fronds compound leaves that are divided into several leaflets
a) The emerging frond is coiled into a fiddlehead that unfurls as it grows
b) leaves may sprout directly form a prostrate stem (bracken and sward ferns) or from upright stems many meters
tall (tropical tree ferns)
4) Ferns are homosporus and the conspicuous leafy fern plant is the sporophyte
a) specialized sporophylls bear sporangia on their undersides: many ferns have sporangia arranged in clusters
called sori and are equipped with spring like devices that catapult spores into the air, where they can be blown
by the wind far from their origin
b) the spore is the dispersal stage
c) the free living gametophyte is small and fragile, requiring a moist habitat
d) water is necessary for fertilization, since flagellated sperm cells must swim form the antheridium to the
archegonium, where fertilization takes place
e) the sporophyte embryo develops protected within the archegonium
E) The coal forests
1) during the carboniferous period, much of the land was covered in shallow seas and swamps.
a. organic rubble of the plants did not decompose and accumulated as peat
b. when later covered by the sea and sediments, heat and pressure transformed the peat into coal
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Ch30: Plant DiersityII: The Evolution of Seed Plants
6. Reproductive adaptations catalyzed the success of the seed plants
A. Three life cycle modifications contributed to seed plant success:
1) Gametophytes became reduced and were retained in the moist reproductive tissue of the sporophyte generation
(they no longer are independent)
2) pollination (male gamete moves in air or on vectors), plants were no longer tied to water for fertilization
3) the evolution of the seed
a) zygote develops into an embryo packaged with a food supply within a protective seed coat
b) seeds replace spores as main means of dispersal
B. In seed plants the seed replace the spore as the main means of dispersing offspring.
1) multicellular seeds are more likely to survive that single celled spores.
2) seed contains an embryo surrounded by a food supply and a tough coat.
3) most seed plants are heterosporus the megasporangia produce megaspores that give rise to eggs, the Microsporangia
produce microspores
4) ovule is made up of megaspore, megasporangium integuments.
5) the female gametophyte develops within the wall of the megaspore and is nourished by the nucleus.
6) if the egg is fertilized the zygote develops into a sporophyte embryo.
7) the resulting sporophyte containing ovule develops into a seed.
C. Pollen ahs become the vehicles for sperm cells in seed plants.
1) are coated with a resilient polymer sporopolenin
2) are carried by wind or animals
3) a pollen grain that recognizes that it is near an ovule will extend a tube through to the ovule.
7. Gymnosperms began to dominate landscapes as the climates became drier at the end of the Paleozoic era
gymnosperms appear in the fossil record much earlier than flowering plants, and they:
1) Lack enclosed chambers in which seeds develop
2) Are grouped into four divisions: Cycadophypyta, Ginkgophyta, Gnetophyta and Coniferophyta.
A. Division Coniferophyta (conifers)
1) Division Coniferophyta is the largest division of gymnosperms:
a) Most are evergreens and include pines, firs , spruces, larches yews junipers, cedars cypresses and redwoods
b) includes some of the tallest (redwoods and some eucalyptus): largest (giant sequoias) and oldest (bristle cone
pine) living organisms
c) most lumber and paper pulp is form conifer wood
2) needle Shaped CONIFER LEAVES ARE ADAPTED TO DRY CONDITIONS
a) Thick cuticle covers the leaf
b) stomata are in pits, reducing water loss
c) despite the shape, needles are megaphylls, as are leaves of all seed plants
B. The life history of a pine
1) The life cycle of pine, a representative conifer, is characterized by the following:
a) the multicellular sporophyte is the most conspicuous stage: the pine tree is a sporophyte, with its sporangia
located on cones.
b) The multicellular gametophyte generation is reduced and develops from haploid spores that are retained
within sporangia
(1) the male gametophyte is the pollen grain, their is no Antheridium
(2) the female gametophyte consists of multicellular nutritive tissue and an archegonium that develops
within an ovule
c) Conifer life cycles are heterosporous: male and female gametophytes develop from different types of spores
produced by separate cones.
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(1) trees of most pine species bear both pollen cones and ovulate cones, which develop on different branches
(2) pollen cones have microsporangia, cells in these sporangia undergo meiosis producing haploid
microspores, small spores that develop into pollen grains which are the male gametophytes.
(3) ovulate cones have megasporangia cells in these sporangia undergo meiosis producing large
megaspores that develop into the female gametophyte. Each ovule initially includes a sporangium
(nucellus) enclosed in protective integuments with a single opening, the microphyle
d) It takes nearly three years to complete the pine life cycle, which progresses through a complicated series of
events to produce mature seeds
(1) Windblown pollen falls onto the ovulate cone and is drawn into the ovule through the microphyle.
(2) the pollen grain germinates in the ovule, forming a pollen tube that begins to digest its way
throughout the nucellus.
(3) The megaspore mother cell in the nucellus undergoes meiosis producing four haploid megaspores, one
of which will survive: it divides repeatedly by mitosis producing the immature female gametophyte
(4) Two or three archegonia, each with an egg, then develop within the multicellular gametophyte
(5) more than a year after pollination, the eggs are ready to be fertilized, two sperm cells have developed and
the pollen tube has grown throughout the nucellus to the female gametophyte
(6) fertilization occurs when one of the sperm nuclei unites with the egg nucleus. All eggs in an ovule
may be fertilized, but usually only one zygote develops into an embryo
(7) the pine embryo or new sporophyte, has a rudimentary root and several embryonic leaves. It is
embedded in the female gametophyte, which nourishes the embryo until it is capable of photosynthesis.
The ovule has developed into a pine see , which consists of an embryo (2n) and its food source (n), and a
surrounding seed coat (2n) derived from the parent tree
(8) Scales of the ovulate cone separate, and the winged seeds are carried by the wind to new locations.
Note, that with the seed plants, the seed has replaced the spore as the mode of dispersal
(9) a seed that lands in a habitable place germinates, its embryo emerging as a pine seedling
C. The History of Gymnosperms
1) Gymnosperms descended from Devonian progymnosperms
a) adaptive radiation during the Carboniferous and Permian periods led to today's divisions
b) During the Permian, Earth became warmer and drier: therefore, lycopods, horsetails and ferns (previously
dominant) were largely replaced by conifers and their relatives, the Cycads
c) This large change marks the end of the Paleozoic era and the beginning of the Mesozoic era. And so we see yet
again a mass extinction of a set of species and another set of species begin to predominate.
8. The evolution of flowers and fruits contributed to the radiation of angiosperms
A. Flowering plants are the most widespread and diverse of the current plant species
1) There is only one division, Anthophyta, with two classes, Monocotyledons (monocots) and Dicotyledons (dicots).
2) Most use insects and animals to transfer pollen, and therefore, are less dependent on wind and have less
random pollination (not as much pollen has to be made, because pollen is directed to the next flower)
B. Vascular tissue became more refined during angiosperm evolution.
1) conifers have tracheids water conducting cells that are
a) and early type of xylem cell
b) elongate, tapered cells that function in Both mechanical support and water movement up the plant
2) Most angiosperms also have vessel elements that are:
a) shorter, wider cells than the more primitive tracheids
b) arranged end to end forming continuous tubes.
c) compared to tracheids, vessel elements are more specialized for conducting water, but less specialized for
support
3) Angiosperm xylem is reinforced by other cell types called fibers which are
a) specialized for support with a thick lignified cell wall
b) Evolved in conifers (note that conifer xylem contains both fibers and tracheids, but not vessel elements)
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C. The flower = the reproductive structure of an angiosperm which is a compressed shoot with four whorls of modified
leaves.
1) Parts of the flower:
a) Sepals - sterile enclose the bud.
b) petals- sterile aid in attracting pollinators
c) Stamen- produces pollen
d) Carpel- evolved form a seed bearing leaf that become rolled into a tube
e) Stigma- part of the carpel that protects the ovules, which develop into seeds after fertilization.
2) The four evolutionary trends in Various Angiosperm Lineages: over time the following happened
a) The number of floral parts have become reduced
b) floral parts have become fused
c) symmetry has changed form radial to bilateral
d) the ovary has dropped below the petal s and sepals, where the ovules are better protected
D. fruit = A ripened ovary that protects dormant seeds and aids in their dispersal: some fruits like apples
incorporate other floral parts along with the ovary
1) Aggregate fruits = several ovaries that are part of the same flower (e.g. Raspberry)
2) Multiple fruit = one that develops from several separate flowers (e.g. pineapple)
3) Modifications of fruits that help disperse seeds include:
a) seeds are within fruits that act as kites or propellers to aid in wind dispersal
b) fruits are modified as burrs that cling to animal fur
c) fruits are edible and seeds pass throughout the digestive tract of herbivores unharmed dispersing seeds miles
away
E. Life cycle of an angiosperm
1) life cycles of angiosperms are heterosporous and the two types of sporangia are found in the flower
a) Microsporangia in anthers produce microspores that form male gametophytes
b) megasporangia in ovules produce megaspores that develop into female gametophytes
2) Immature male gametophytes
a) are pollen grains which develop within the anthers of stamens
b) each pollen grain has two haploid nuclei that will participate in double fertilization characteristic of
angiosperms
3) Female gametophytes:
a) do not produce an archegonium
b) are located within an ovule
c) consist of only a few cells- an embryo sac with eight haploid nuclei in seven cells ( a large central cell has two
haploid nuclei
d) one of the cells is the egg
4) an outline of the angiosperm life cycle follows:
a) pollen from the anther lands on the sticky stigma at the carple's tip: most flowers do not self pollinate, but have
mechanisms to ensure cross-pollination
b) the pollen grain germinates on the stigmata by growing a pollen tube down the style of the carpel
c) when it reaches the ovary, the pollen tube grows through its microphyle and discharges two sperm cells into the
embryo sac
d) double fertilization occurs as one sperm nucleus unites with the egg to form a diploid zygote: the other sperm
nucleus fusses with two nuclei in the embryo sac's central cell to form triploid (3n) endosperm
e) after double fertilization, the ovule matures into a seed
5) The seed is a mature ovule, consisting of
a) Embryo. The zygote develops into an embryo with a rudimentary root and one or two cotyledons or seed
leaves
b) Endosperm> The triploid nucleus in the embryo sac divides repeatedly forming triploid endosperm, rich in
starch and other food reserves
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c) Seed coat. This is derived form the integuments (outer layers of the ovules)
6) Monocots use endosperm differently
a) monocot seeds store most of the food in the endosperm
b) dicots generally restock most of the nutrients in the developing cotyledons
7) In a suitable environment the seed coat ruptures and the embryo emerges as a seedling, using the food stored in the
endosperm and cotyledons
F. The rise of Angiosperms
1) angiosperms showed a relatively sudden appearance in the fossil record with no clear transitional links to ancestors
a) earliest fossils are early Cretaceous (approximately 120mya)
b) by the end of the Cretaceous (65mya) angiosperms became dominant, as the are today
2) Thee two theories about the sudden appearance are
a) Artifact of an imperfect fossil record: angiosperms originated where fossilization was unlikely
b) punctuated equilibrium: angiosperms did evolve and radiate relatively abruptly
3) Angiosperms perhaps evolved form seed ferns, and extinct group of unspecialized gymnosperms
G. Relationships between angiosperms and animals
1) Terrestrial plants and animals have coevolved a consequence of their interdependence
2) Coevolution = reciprocal evolutionary responses amount two or more interacting species: adaptive change in one
species is in response to evolutionary change in the other species
3) Coevolution between angiosperms and their pollinators let to diversity of flowers
a) some pollinators are specific for a particular flower. The pollinator has a monopoly on a food source and
guarantees the flower's pollen will pollinate a flower of the same species
b) often , the relationship between angiosperms and their pollinators is not species specific: a pollinator may not
depend exclusively on tone flower species or a flower species may not depend exclusively on one species of
pollinator, However flower color fragrance and structure are usually adaptations for types of pollinators, such
as various species of bees or hummingbirds
4) Edible fruits of angiosperms have coevolved with animals that can disperse seeds. Animals become attracted
to ripening fruits as they
a) become softer, form fragrant and higher in sugar
b) change to a color that attracts birds and mammals, animals large enough to disperse the seeds
H. Angiosperms and agriculture
1)Angiosperms provide nearly all our food
a) fruit
b) vegetable crops
c) grains, such as corn, rice, wheat
3) Flowering plants are also used for other purposes such as
a) fiber
b) medication
c) perfume
d) decoration
4) Through agriculture, humans have influenced plant evolution by artificially selecting for plants that improved the
quantity and quality of foods and other crops
a) many of our agricultural plants are so genetically removed form their origins that they probably could not
survive in the wild
b) as a consequence, cultivated crops that require an intervention to water, fertilizer, provide protection form
insects and disease, and even to plant their seeds, are vulnerable to natural and human caused distress
9. Plant diversity is a nonrenewable resource
A. Plant diversity is a nonrenewable resource, and the irrevocable extinction of plant species is occurring at an
unprecedented rate
1) the exploding human population demands space and natural resources
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2) the toll of habitat destruction is greatest in the tropics because this is where
a) most species live
b) more than half the human population lives and human population growth is fastest
c) most deforestation is caused by slash and burn clearing for agriculture
B. As the forest disappears, so do thousands of plant and animal species
1) habitat destruction also endangers animal species that depend on plants in the tropical rainforest
2) habitat destruction by humans has not been limited to the tropics. Europeans eliminated most of their forests
centuries ago, and in North America, destruction of habitat is endangering many species
C. Their are many reasons to value plant diversity and to find ways to protect it
1) Ecosystems are living treasures that can regenerate only slowly
2) humans depend on plants for products such a medicines, food, and building materials
3) we still know so little of the 2500,000 known plant species food ag. is based on 2 dozen
Quiz top
1. In the alternation of generations we see an alternation of the sporophyte and gametophyte generations. Why is it to an
organisms advantage to produce a multicellular sporophyte that then goes on to divide and produce gametophytes?
A) Sporophytes tend to be more resistant to sunlight and desiccation than gametophytes
B) Sporophytes divide into an 8 celled stage and produce gametophytes
C) A larger sporophyte is able to make many more gametophytes per fertilization event
D) A larger sporophyte can be made without fertilization
2. Which of the following are correct
A) ferns have megaphylls
B) lycopods have microphylls
C) lycopods have megaphylls
D) ferns have microphylls
E) Megaphylls have branching veins and microphylls have only one vein.
3. The dispersal form of a fern is the
A) seed
B) spore
C) sperm
D) sori
E) gemmae
4. Gymnosperm are different from angiosperm in that:
A) gymnosperms have tracheids and angiosperm have vessel elements
B) gymnosperm use insects and animals for pollination and angiosperm use the wind all the time
C) gymnosperm do not have fibers and angiosperm do have fibers
D) gymnosperm leaves are microphylls and angiosperm are megaphylls
E) gymnosperm do not have roots
5. Plant conservation:
A) tries to keep as much land covered by plants as possible?
B) Tries to protect the diversity of plants that support animals
Lecture notes.
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1) Know the differences between the various plant types.
differences in alternation of generations
examples of the types
advantages over the previous
environment that they inhabit.
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Plant diversity: A combination of chapters 29 and 30
Plants are : multicelled photoautorrophs similar to Algae.
Photosynthetic pigments: chrlorphyll A,B, Carotinoids
Food storage: Starch in plastids.
Plants ate thought to be closely related to green algae. Why?
Charophytes: probable ancestors to modern plants
Cell wall
Pigmentation
Chloroplasts (DNA and membrane composition)
Cell organelles (peroxisomes)
Alternation of generations evolved independently (why?)
Plants have 2 main obstacles to overcome to colonize land.
Dispersing gametes in a nonaquatic environment
Embryo need to be protected form desiccation
Certain Adaptations allowed plants to colonize land.
The cuticle
Stomata for gas exchange
Stiffening produces such as lignin and sporopollenin (secondary
products)
A way to combine gametes without the presence of water or reduced
presence of water.
Alternation of Generations
Gametangia- early plants that produced gametes within these structures
Embryophytes- embryos are not retained within the parent tissue.
Many early plants have multicellular haploid stages.
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Be able to write out a prototypical Alternation of generations.
There are 4 major periods of plant evolution
1. plants evolve from aquatic ancestors 425mya
2. seedless vascular plants (ferns) 400mya
3. the seed (embryo, food, protection) 350mya
4. flowering plants 130mya
Know the major divisions of plants.
Non vascular (move liquid by diffusion)
Bryophyta (mosses)
Hepatophyta (liverworts)
Antherocerphyta (horn worts)
Vascular seedless
Psilophyta (wisk ferns)
Pterophyta (ferns)
Lycophyta (club moss)
Sphenophyta (horse tails)
Vascular seed plants
Coniferophyta (conifers)
Cycadophyta (cycads)
Ginkgophyta (ginko)
Anthophyta (flowering plants.
Know characteristics, examples and where these things live
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